'''
nbody sim
'''
from time import time

# Pulled from http://shootout.alioth.debian.org/u64q/benchmark.php?test=nbody&lang=python&id=4
# Contributed by Kevin Carson.
# Modified by Tupteq, Fredrik Johansson, and Daniel Nanz.


def main():
	if PYTHON=='PYTHONJS':
		pythonjs.configure( direct_operator='+' )
		pythonjs.configure( direct_operator='*' )
		pythonjs.configure( direct_keys=True )
		pass

	times = test_nbody( 3 )
	avg = sum( times ) / 3.0
	print( avg )




def combinations(l):
	"""Pure-Python implementation of itertools.combinations(l, 2)."""
	result = []
	for x in range(len(l) - 1):
		ls = l[x+1:]
		for y in ls:
			result.append((l[x],y))
	return result


PI = 3.14159265358979323
SOLAR_MASS = 4 * PI * PI
DAYS_PER_YEAR = 365.24

BODIES = {
	'sun': ([0.0, 0.0, 0.0], [0.0, 0.0, 0.0], SOLAR_MASS),

	'jupiter': ([4.84143144246472090e+00,
				 -1.16032004402742839e+00,
				 -1.03622044471123109e-01],
				[1.66007664274403694e-03 * DAYS_PER_YEAR,
				 7.69901118419740425e-03 * DAYS_PER_YEAR,
				 -6.90460016972063023e-05 * DAYS_PER_YEAR],
				 9.54791938424326609e-04 * SOLAR_MASS),

	'saturn': ([8.34336671824457987e+00,
				4.12479856412430479e+00,
				-4.03523417114321381e-01],
			   [-2.76742510726862411e-03 * DAYS_PER_YEAR,
				4.99852801234917238e-03 * DAYS_PER_YEAR,
				2.30417297573763929e-05 * DAYS_PER_YEAR],
				2.85885980666130812e-04 * SOLAR_MASS),

	'uranus': ([1.28943695621391310e+01,
				-1.51111514016986312e+01,
				-2.23307578892655734e-01],
			   [2.96460137564761618e-03 * DAYS_PER_YEAR,
				2.37847173959480950e-03 * DAYS_PER_YEAR,
				-2.96589568540237556e-05 * DAYS_PER_YEAR],
				4.36624404335156298e-05 * SOLAR_MASS),

	'neptune': ([1.53796971148509165e+01,
				 -2.59193146099879641e+01,
				 1.79258772950371181e-01],
				[2.68067772490389322e-03 * DAYS_PER_YEAR,
				 1.62824170038242295e-03 * DAYS_PER_YEAR,
				 -9.51592254519715870e-05 * DAYS_PER_YEAR],
				 5.15138902046611451e-05 * SOLAR_MASS) }





def advance(dt, n, bodies, pairs):
	for i in range(n):
		for pair in pairs:
			p1,p2 = pair
			vec1, v1, m1 = p1
			vec2, v2, m2 = p2
			x1, y1, z1 = vec1
			x2, y2, z2 = vec2

			dx = x1 - x2
			dy = y1 - y2
			dz = z1 - z2
			mag = dt * ((dx * dx + dy * dy + dz * dz) ** (-1.5))
			b1m = m1 * mag
			b2m = m2 * mag
			v1[0] -= dx * b2m
			v1[1] -= dy * b2m
			v1[2] -= dz * b2m
			v2[0] += dx * b1m
			v2[1] += dy * b1m
			v2[2] += dz * b1m

		for w in bodies:
			r, v, m = w
			r[0] += dt * v[0]
			r[1] += dt * v[1]
			r[2] += dt * v[2]


def report_energy(bodies, pairs):
	e = 0.0
	for pair in pairs:
		p1,p2 = pair
		vec1, v1, m1 = p1
		vec2, v2, m2 = p2
		x1, y1, z1 = vec1
		x2, y2, z2 = vec2

		dx = x1 - x2
		dy = y1 - y2
		dz = z1 - z2
		e -= (m1 * m2) / ((dx * dx + dy * dy + dz * dz) ** 0.5)

	for w in bodies:
		r, v, m = w
		vx, vy, vz = v
		#e += m * (vx * vx + vy * vy + vz * vz) / 2.0  ## TODO fix this
		a = vx * vx + vy * vy + vz * vz
		a /= 2.0
		e += m * a
	return e


def offset_momentum(ref, bodies, px=0.0, py=0.0, pz=0.0):
	for w in bodies:
		r, v, m = w
		vx, vy, vz = v

		px -= vx * m
		py -= vy * m
		pz -= vz * m
	(r, v, m) = ref
	v[0] = px / m
	v[1] = py / m
	v[2] = pz / m


def test_nbody(iterations):
	SYSTEM = []
	for key in BODIES: SYSTEM.append( BODIES[key] )
	PAIRS = combinations(SYSTEM)

	times = []
	for _ in range(iterations):
		t0 = time()
		start_e = report_energy( SYSTEM, PAIRS )
		advance(0.01, 20000, SYSTEM, PAIRS)
		end_e = report_energy( SYSTEM, PAIRS )
		t1 = time()
		print('#start energy:', start_e)
		print('#end energy:', end_e)
		times.append(t1 - t0)
	return times


